1. Technical Field
The present invention relates to a polymer having hydroxyl and carboxyl groups and also to its production process and use.
2. Background Art
As the polymer having hydroxyl and carboxyl groups, known are, for example, a modified polyvinyl alcohol and a polyhydroxyacrylic acid.
The modified polyvinyl alcohol is produced by copolymerizing vinyl acetate and an acrylic acid ester and then saponifying the resulting copolymer.
The polyhydroxyacrylic acid is produced by polymerizing .alpha.-hydroxyacrylic acid and then removing the by-product salts.
A partially lactonized product from the modified polyvinyl alcohol and the polyhydroxyacrylic acid is also known. This partially lactonized product is obtained by reacting part of the hydroxyl groups of said alcohol with part of the carboxyl groups of said acid to form lactone rings.
However, the modified polyvinyl alcohol is inferior in dispersibility or lacks a chelating ability or a viscosity-stabilizing ability. In addition, the partially lactonized product from the modified polyvinyl alcohol and the polyhydroxyacrylic acid also is inferior in dispersibility or lacks a chelating ability or a viscosity-stabilizing ability.
There is also a process for producing the modified polyvinyl alcohol which comprises a saponification step of carrying out a reaction which involves elimination of an ester. However, this saponification step is industrially disadvantageous, because it involves complex procedures and because production costs are expensive.
The modified polyvinyl alcohol, the polyhydroxyacrylic acid and their partially lactonized product were proposed for uses as a detergent builder, a pigment-dispersing agent, a cement-dispersing agent, a stabilizer for hydrogen peroxide, and so on.
However, as to the polyhydroxyacrylic acid, .alpha.-hydroxyacrylic acid of a starting material is expensive and in addition the production process is industrially disadvantageous because it involves complex procedures. Therefore, the polyhydroxyacrylic acid is not practically used for the detergent builder and the pigment-dispersing agent.
When used as detergent builders, the modified polyvinyl alcohol and the partially lactonized product provide inferior results when compared with conventional sodium polyacrylate with regard to an improving effect upon washing-power.
When used as pigment-dispersing agents, the modified polyvinyl alcohol and the partially lactonized product provide inferior results when compared with conventional sodium polyacrylate with regard to dispersibility and a viscosity-stabilizing ability. Because of this, the viscosity of a pigment dispersion is high and increases with time. Therefore handling is hard.
When used as cement-dispersing agents, the modified polyvinyl alcohol, the polyhydroxyacrylic acid and their partially lactonized product provide inferior results when compared with a conventional sodium naphthalenesulfonate-formalin condensation product or sodium ligninsulfonate with regard to an ability to prevent slump loss.
When the modified polyvinyl alcohol and the partially lactonized product are used as stabilizers for hydrogen peroxide, hydrogen peroxide easily decomposes in comparison with the case of using conventional sodium polyacrylate.
The modified polyvinyl alcohol, the polyhydroxyacrylic acid and their partially lactonized product have an film-forming ability. However, they have no especially useful character other than that the film formed from them easily dissolves in water.